On Wed, Dec 2, 2020 at 1:51 PM Jason Wang <jasow...@redhat.com> wrote: > > > On 2020/12/2 下午12:53, Parav Pandit wrote: > > > >> From: Yongji Xie <xieyon...@bytedance.com> > >> Sent: Wednesday, December 2, 2020 9:00 AM > >> > >> On Tue, Dec 1, 2020 at 11:59 PM Parav Pandit <pa...@nvidia.com> wrote: > >>> > >>> > >>>> From: Yongji Xie <xieyon...@bytedance.com> > >>>> Sent: Tuesday, December 1, 2020 7:49 PM > >>>> > >>>> On Tue, Dec 1, 2020 at 7:32 PM Parav Pandit <pa...@nvidia.com> wrote: > >>>>> > >>>>> > >>>>>> From: Yongji Xie <xieyon...@bytedance.com> > >>>>>> Sent: Tuesday, December 1, 2020 3:26 PM > >>>>>> > >>>>>> On Tue, Dec 1, 2020 at 2:25 PM Jason Wang <jasow...@redhat.com> > >>>> wrote: > >>>>>>> > >>>>>>> On 2020/11/30 下午3:07, Yongji Xie wrote: > >>>>>>>>>> Thanks for adding me, Jason! > >>>>>>>>>> > >>>>>>>>>> Now I'm working on a v2 patchset for VDUSE (vDPA Device in > >>>>>>>>>> Userspace) [1]. This tool is very useful for the vduse device. > >>>>>>>>>> So I'm considering integrating this into my v2 patchset. > >>>>>>>>>> But there is one problem： > >>>>>>>>>> > >>>>>>>>>> In this tool, vdpa device config action and enable action > >>>>>>>>>> are combined into one netlink msg: VDPA_CMD_DEV_NEW. But > >>>>>>>>>> in > >>>> vduse > >>>>>>>>>> case, it needs to be splitted because a chardev should be > >>>>>>>>>> created and opened by a userspace process before we enable > >>>>>>>>>> the vdpa device (call vdpa_register_device()). > >>>>>>>>>> > >>>>>>>>>> So I'd like to know whether it's possible (or have some > >>>>>>>>>> plans) to add two new netlink msgs something like: > >>>>>>>>>> VDPA_CMD_DEV_ENABLE > >>>>>> and > >>>>>>>>>> VDPA_CMD_DEV_DISABLE to make the config path more flexible. > >>>>>>>>>> > >>>>>>>>> Actually, we've discussed such intermediate step in some > >>>>>>>>> early discussion. It looks to me VDUSE could be one of the users of > >> this. > >>>>>>>>> Or I wonder whether we can switch to use anonymous > >>>>>>>>> inode(fd) for VDUSE then fetching it via an VDUSE_GET_DEVICE_FD > >> ioctl? > >>>>>>>> Yes, we can. Actually the current implementation in VDUSE is > >>>>>>>> like this. But seems like this is still a intermediate step. > >>>>>>>> The fd should be binded to a name or something else which > >>>>>>>> need to be configured before. > >>>>>>> > >>>>>>> The name could be specified via the netlink. It looks to me > >>>>>>> the real issue is that until the device is connected with a > >>>>>>> userspace, it can't be used. So we also need to fail the > >>>>>>> enabling if it doesn't > >>>> opened. > >>>>>> Yes, that's true. So you mean we can firstly try to fetch the fd > >>>>>> binded to a name/vduse_id via an VDUSE_GET_DEVICE_FD, then use > >>>>>> the name/vduse_id as a attribute to create vdpa device? It looks fine > >>>>>> to > >> me. > >>>>> I probably do not well understand. I tried reading patch [1] and > >>>>> few things > >>>> do not look correct as below. > >>>>> Creating the vdpa device on the bus device and destroying the > >>>>> device from > >>>> the workqueue seems unnecessary and racy. > >>>>> It seems vduse driver needs > >>>>> This is something should be done as part of the vdpa dev add > >>>>> command, > >>>> instead of connecting two sides separately and ensuring race free > >>>> access to it. > >>>>> So VDUSE_DEV_START and VDUSE_DEV_STOP should possibly be avoided. > >>>>> > >>>> Yes, we can avoid these two ioctls with the help of the management tool. > >>>> > >>>>> $ vdpa dev add parentdev vduse_mgmtdev type net name foo2 > >>>>> > >>>>> When above command is executed it creates necessary vdpa device > >>>>> foo2 > >>>> on the bus. > >>>>> When user binds foo2 device with the vduse driver, in the probe(), > >>>>> it > >>>> creates respective char device to access it from user space. > >>>> > >>> I see. So vduse cannot work with any existing vdpa devices like ifc, mlx5 > >>> or > >> netdevsim. > >>> It has its own implementation similar to fuse with its own backend of > >>> choice. > >>> More below. > >>> > >>>> But vduse driver is not a vdpa bus driver. It works like vdpasim > >>>> driver, but offloads the data plane and control plane to a user space > >>>> process. > >>> In that case to draw parallel lines, > >>> > >>> 1. netdevsim: > >>> (a) create resources in kernel sw > >>> (b) datapath simulates in kernel > >>> > >>> 2. ifc + mlx5 vdpa dev: > >>> (a) creates resource in hw > >>> (b) data path is in hw > >>> > >>> 3. vduse: > >>> (a) creates resources in userspace sw > >>> (b) data path is in user space. > >>> hence creates data path resources for user space. > >>> So char device is created, removed as result of vdpa device creation. > >>> > >>> For example, > >>> $ vdpa dev add parentdev vduse_mgmtdev type net name foo2 > >>> > >>> Above command will create char device for user space. > >>> > >>> Similar command for ifc/mlx5 would have created similar channel for rest > >>> of > >> the config commands in hw. > >>> vduse channel = char device, eventfd etc. > >>> ifc/mlx5 hw channel = bar, irq, command interface etc Netdev sim > >>> channel = sw direct calls > >>> > >>> Does it make sense? > >> In my understanding, to make vdpa work, we need a backend (datapath > >> resources) and a frontend (a vdpa device attached to a vdpa bus). In the > >> above > >> example, it looks like we use the command "vdpa dev add ..." > >> to create a backend, so do we need another command to create a frontend? > >> > > For block device there is certainly some backend to process the IOs. > > Sometimes backend to be setup first, before its front end is exposed. > > "vdpa dev add" is the front end command who connects to the backend > > (implicitly) for network device. > > > > vhost->vdpa_block_device->backend_io_processor (usr,hw,kernel). > > > > And it needs a way to connect to backend when explicitly specified during > > creation time. > > Something like, > > $ vdpa dev add parentdev vdpa_vduse type block name foo3 handle <uuid> > > In above example some vendor device specific unique handle is passed based > > on backend setup in hardware/user space. > > > > In below 3 examples, vdpa block simulator is connecting to backend block or > > file. > > > > $ vdpa dev add parentdev vdpa_blocksim type block name foo4 blockdev > > /dev/zero > > > > $ vdpa dev add parentdev vdpa_blocksim type block name foo5 blockdev > > /dev/sda2 size=100M offset=10M > > > > $ vdpa dev add parentdev vdpa_block filebackend_sim type block name foo6 > > file /root/file_backend.txt > > > > Or may be backend connects to the created vdpa device is bound to the > > driver. > > Can vduse attach to the created vdpa block device through the char device > > and establish the channel to receive IOs, and to setup the block config > > space? > > > I think it can work. > > Another thing I wonder it that, do we consider more than one VDUSE > parentdev(or management dev)? This allows us to have separated devices > implemented via different processes. > > If yes, VDUSE ioctl needs to be extended to register/unregister parentdev. >
Yes, we need to extend the ioctl to support that. Now we only have one parentdev represented by /dev/vduse. Thanks, Yongji
